Colonoscopy: Prep, What Happens, Polyps and Results
A colonoscopy uses a flexible camera to look inside your colon and rectum, and it can remove polyps during the same test. The USPSTF advises colorectal cancer screening from age 45 through 75, with colonoscopy every 10 years if the result is normal. The exam usually takes less than an hour, and you are sedated. The hardest part for most people is the bowel prep the day before.
Why it is done
A colonoscopy is used for two main reasons: routine screening when you feel fine, and looking for the cause of a problem. It can check blood in the stool, black stools, a change in bowel habits, belly pain, weight loss or low iron. It is also used to follow up past polyps, colorectal cancer or inflammatory bowel disease.
If a stool test or blood test comes back positive, you need a colonoscopy to find out why. The screening only works if this step happens. The American Cancer Society (ACS) advises having it, preferably within 6 months of the positive result.
Screening ages
| Age | USPSTF advice |
|---|---|
| 45 to 49 | Screen (grade B) |
| 50 to 75 | Screen (grade A) |
| 76 to 85 | Decide with your doctor, based on your health, past screening and preferences (grade C) |
| Over 85 | Screening should stop |
The USPSTF is the US Preventive Services Task Force, an independent expert panel. ACS, in its 2026 update, also advises starting at 45 for people at average risk and continuing through 75 if life expectancy is over 10 years.
Colonoscopy is one of several choices. Others include a yearly FIT stool test, a stool DNA test every 1 to 3 years, and CT colonography or flexible sigmoidoscopy every 5 years. Colonoscopy lets the doctor find and remove polyps in the same exam.
You may need to start earlier or go more often if you have a family history of colorectal cancer, inflammatory bowel disease, or an inherited condition such as Lynch syndrome. Ask your doctor.
Bowel prep
Your colon must be empty for the doctor to see. Follow the written instructions from your own clinic, because products and timing differ. A typical plan looks like this:
| When | What to do |
|---|---|
| 2 weeks or more before | Ask about blood thinners. Examples are warfarin, clopidogrel, apixaban and rivaroxaban. Do not stop them on your own |
| About 1 week before | Ask about diabetes drugs and GLP-1 drugs such as semaglutide. Stop iron pills if told to |
| Up to 3 days before | Eat low-fiber foods. Avoid nuts, seeds, popcorn, beans, raw vegetables and whole grains |
| The day before | Clear liquids only, as your instructions say. No solid food |
| The evening before | First part of the prep laxative |
| The morning of the test | Second part, often about 6 hours before. Stop all liquids when told, often about 3 hours before |
Clear liquids include water, clear broth, black coffee or tea (no milk or creamer), strained juice without pulp, and yellow, green or blue sports drinks, gelatin or ice pops. Avoid anything red, purple or orange, and alcohol.
Expect frequent watery diarrhea within hours, so stay near a bathroom. It helps to chill the prep if your instructions allow it.
If you cannot finish the prep, call the clinic. Do not just skip it. If the colon is not clean, the exam may need to be repeated. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) advises calling if side effects stop you from finishing. If you have diabetes or kidney or heart disease, or are on chemo, ask for specific instructions.
Arrange for an adult to take you home. You cannot drive after sedation.
What happens during the test
- You get medicine through an IV so you are relaxed and comfortable. Most people do not feel pain or remember the test.
- You lie on your side. The doctor, usually a gastroenterologist, passes a flexible tube with a camera through the anus.
- Air or carbon dioxide opens the colon so the doctor can see.
- The doctor examines the lining carefully as the tube is withdrawn.
- Polyps can be removed and tissue sampled (a biopsy). You will not feel this.
The test usually takes less than an hour. You stay about 30 to 60 minutes afterward. You may have cramps or bloating for the first hour. Most people are back to normal diet and activity by the next day.
Polyps: what they mean
A polyp is a growth on the lining of the colon. Finding one is common, and most are not cancer. Removing them is one way colonoscopy prevents cancer. A pathologist checks each one under a microscope, and results can take a few days or longer.
| Type | What it means |
|---|---|
| Hyperplastic | Usually harmless |
| Tubular adenoma | A pre-cancer. It should be removed |
| Villous or tubulovillous adenoma | A pre-cancer with higher risk. Larger ones are more likely to contain cancer |
| Serrated polyp | A saw-toothed polyp that can become cancer. It should be removed completely |
| High-grade dysplasia | Cells that look very abnormal. May mean a sooner follow-up |
A pre-cancer is not cancer. It means the polyp could have become cancer if it had been left in place, and now it is gone. If a polyp could not be fully removed, or cancer is found, your doctor will discuss next steps. These may include surgery, staging and a referral to a specialist. See colorectal cancer staging and cancer surgery.
When to repeat a colonoscopy
These intervals are from the 2020 US Multi-Society Task Force guidance. They assume a complete exam with a good prep. They do not apply if you have an inherited syndrome, inflammatory bowel disease, or a personal or family history of colorectal cancer.
| What was found | Next colonoscopy |
|---|---|
| Normal | 10 years |
| Up to 20 small hyperplastic polyps (under 10 mm) | 10 years |
| 1 to 2 small tubular adenomas (under 10 mm) | 7 to 10 years |
| 3 to 4 small tubular adenomas | 3 to 5 years |
| 5 to 10 small tubular adenomas | 3 years |
| Adenoma 10 mm or larger, or with villous features or high-grade dysplasia | 3 years |
| More than 10 adenomas | 1 year, and consider genetic testing |
| 1 to 2 small sessile serrated polyps | 5 to 10 years |
Your report may give a different date for good reasons, such as polyp size, how the polyp was removed or the quality of the prep. Follow the date your own doctor gives you. Ask for a copy of the report so you know your interval.
Risks
Serious problems are uncommon. The USPSTF reports about 14.6 cases of major bleeding and 3.1 perforations (tears in the colon wall) per 10,000 screening colonoscopies. NIDDK gives similar figures. Most occur in older people or when polyps are removed. Other risks include reactions to sedation, which can affect breathing or the heart, and, very rarely, infection. A tear may need surgery.
Light bleeding after polyp removal or biopsy is normal. Delayed bleeding can happen up to 2 weeks afterward.
Get medical care right away after a colonoscopy if you have: severe belly pain; a fever; bloody bowel movements that do not improve; bleeding from the anus that does not stop; or dizziness or weakness.
Frequently asked questions
At what age should I get my first colonoscopy?
Most people at average risk should begin colorectal cancer screening at age 45. Colonoscopy is one option. You may need to begin earlier if you have a family history or an inherited condition.
Does a colonoscopy hurt?
Usually not. You receive medicine through an IV and usually will not feel pain or remember the test. Some cramping or bloating is common for about an hour afterward.
How long does a colonoscopy take?
The test usually takes less than an hour. Plan for more time at the center, including about 30 to 60 minutes of recovery. You need someone to take you home.
Can I drink coffee before a colonoscopy?
Usually yes, if it is black, with no milk or creamer, during your clear-liquid period. Stop all liquids when your instructions tell you to, often about 3 hours before.
How long should I wait if a polyp was found?
It depends on the number, size and type of polyps. It may be 7 to 10 years after 1 or 2 small tubular adenomas, or 3 years after larger or higher-risk ones. Your doctor will give you a date.
Does a tubular adenoma mean I have cancer?
No. It is a pre-cancer. Removing it lowers your risk. Your doctor will use the report to decide when you need your next colonoscopy.
What if my stool test was positive?
You need a colonoscopy to find the cause. A positive result does not mean you have cancer. The American Cancer Society advises having the follow-up colonoscopy, preferably within 6 months.
What should I eat after a colonoscopy?
Most people can return to a normal diet by the next day. Follow any special instructions you are given, especially if polyps were removed.
Sources
- US Preventive Services Task Force: Colorectal Cancer Screening (2021)
- American Cancer Society: Colorectal Cancer Screening Guideline Update (2026)
- National Institute of Diabetes and Digestive and Kidney Diseases: Colonoscopy
- MedlinePlus: Colonoscopy
- American Cancer Society: Screening Tests for Colorectal Cancer
- American Cancer Society: Understanding Your Pathology Report: Colon Polyps
- Cleveland Clinic: Colonoscopy Bowel Preparation Using SUPREP
- American Family Physician: Colonoscopy Follow-up, U.S. Multi-Society Task Force Updates Recommendations
- US Multi-Society Task Force: Colonoscopy follow-up recommendations (published summary)
This page is general information, not medical advice. Your care team knows your situation and should guide your decisions.